I searched around for this and was surprised how little data I could find. I want to know the population of all tribes that Genghis Khan had under his control when he became the Great Khan (1206). Hasn't there been some study and some estimate by any historians?

I could probably come up with an area-based estimate, but a tribal or ethnic based one would be tougher.
– T.E.D.♦Apr 20 '18 at 20:31

2

@T.E.D., I think it's possible to estimate based on his army size, commonly estimated between 100k and 130k. Given that under his control most male Mongols of appropriate age were warriors, multiply the army size by 4 or 5 for the total population somewhere between 400k and 650k.
– MichaelApr 20 '18 at 20:51

@Michael But are we sure that all fighting-age males went along on every campaign? Wouldn't there be some left behind for a variety of duties like administration and guarding against attacks from a different region?
– DrZ214Apr 20 '18 at 20:53

Depending on the year there were also numerous campaigns, so one army group was not his entire army.
– ed.hankApr 20 '18 at 21:33

@Michael - Well, your estimate appears to be roughly consistent with the actual numbers I dug up, and they used your exact method to arrive at it, so I've sheepishly deleted my quibble with your methods. :-)
– T.E.D.♦Apr 20 '18 at 21:44

1 Answer
1

... the demographic base was of the same order of magnitude about 800,000
when in the 13th century Genghis Khan set out from Mongolia to
conquer the world, and it was still in the same band in fact slightly lower, about
600,000 when the Chinese established control over the country in the
18th century.

Here's what they wrote about their sources:

A. K. Validi (quoted by • Russell, p. 87) suggests a figure of
0.5m for Mongolia in the 6th 9th centuries AD. This is no more than
an informed guess, for only one figure of use survives from the
pre-modern period: the size of Genghis Khan's army. This was established at 129,000 men, with H. D. Martin, The Rise of Chingis Khan
and His Conquest of North China (1950). p. 14. considers compatible
with a Mongolian population of around 0.75m. C. R. Bawden (The
Modern History of Mongolia (1968)) quotes a mid-19th-century Russian
estimate of ‘not much over 0.5m,‘ and G. S. Murphy (Soviet Mongolia
(1966)) one made in 1918 of about 0.7m. The first census was taken in
1956, the second in 1969.

This implies to be there's a great deal of guesswork in this number based on the only historically reported fact available (a report of the size of his army). So it should probably be taken as no more than a rough order of magnitude estimate.